The present invention relates to an information processing system and method, and more particularly, to an information processing system and a method which manages an alternative path when the system accesses an I/O device.
Referring to FIG. 17, in a conventional alternative path control system of this type, systems 401 and 402 each have independent I/O buses and a path for transferring a request between the systems. System 401 includes CPU 411, transfer control element 412, Peripheral Component Interconnect (PCI) bridges 413 and 414, I/O buses 415 and 416, and Small Computer Serial Interface (SCSI) card 417. System 402 includes CPU 421, transfer control element 422, PCI bridges 423 and 424, I/O buses 425 and 426, and SCSI card 427.
CPUs 411 and 421 are processors that perform information processing independently of each other. Transfer control elements 412 and 422 receive I/O requests outputted from CPUs 411 and 421, determine which ports of their own system or other systems the I/O requests are to be transferred to, and transfer the requests. PCI bridges 413, 414, 423 and 424 receive requests from transfer control elements 412 and 422, convert them into the protocol of a PCI bus and transfer them. I/O buses 415, 416, 425 and 426 are PCI buses that connect I/O devices. SCSI cards 417 and 427 are SCSI control cards that are connected to the PCI buses. A disk device 43 is an external storage connected to SCSI cards 417 and 427.
In this conventional system, when SCSI card 417 is accessed, for example, it is necessary to always use a path including PCI bridge 413. This creates problem because it is impossible to access SCSI card 417 if PCI bridge 413 fails.
To address this problem of the path for an I/O access, for example, SCSI cards 417 and 427 are connected to I/O buses 415 and 425, respectively. Specifically, two I/O cards (SCSI cards) on different I/O buses are cross-connected to an external I/O device such as disk device 43 as shown in FIG. 17. Thus, if SCSI card 417 cannot be used because of a failure in PCI bridge 413, an access path to disk device 43 is secured by going through SCSI card 427 provided under PCI bridge 423 of other system 402.
Another alternative path selecting system when a failure occurrs is described in Japanese laid-open publication Hei No.8-212147. This publication discloses a channel processing apparatus which manages and controls channel paths for selectively transferring information between a CPU and one of the I/O devices. The apparatus replaces the physical channel number and the logical channel number related to a channel path, on which a failure has occurred, with the physical channel number and the logical channel number related to a channel path not used by the operating system.
Japanese laid-open publication Hei No.3-105540 discloses an input/output control method that makes it possible to perform an input/output request even when a measure is being taken to cope with channel trouble, by identifying an input/output path as being faulty and notifying an I/O processor, which is hardware for controlling a channel, not to select the faulty input/output path.
These methods cannot be applied to the system shown in FIG. 17, because the configurations are different.
In above-described conventional system, two I/O cards, each of which is mounted to each independent apparatus, are required for switching over a path for one device, such as a disk device or the like. A problem is caused because the number of kinds of I/O cards which are mounted in an apparatus is restricted.
Moreover, the above-described conventional system is applicable only to an I/O device having two or more input ports. This creates another problem because it is impossible to apply the above-described configuration to an I/O device having only one port.
Another problem is caused because the system requires dedicated support software. Such dedicated support software is used for recognizing each I/O card which forms crossing paths and determining which path is to be used when one of the paths cannot be used because of a failure on any part of the path.
An object of the invention is to provide an alternative path control system which creates an alternative path to an I/O device without using a plurality of I/O cards.
Another object of the invention is to provide an alternative path control system that is not dependent on the number of ports of I/O devices and the like to be connected.
Another object of the invention is to provide an alternative path control system which does not require any special software for handling the alternative path. Specifically, in the alternative path of the invention, a request does not need information which designates the alternative path.
According to one aspect of the present invention, an information processing system is provided which includes: a first system in which a first device is provided and produces a request for the first device, wherein the first system includes a first element which is connected to the first device and has at least two inputs, a second element which receives the request and outputs the request to one of the inputs of the first element, and a third element which outputs the request to the second element; a second system in which a second device is provided and which has a fourth element which is connected to the second device and has at least two inputs, a fifth element which receives the request and outputs the request to one of the inputs of the fourth element, and a sixth element which outputs the request to the fifth element; wherein the third element outputs the request to the sixth element when there is a failure on the path from the third element to the first element; and wherein the fifth element outputs the request to one of the inputs of the first element.
According to another aspect of the present invention, an information processing system is provided which includes: a first system to which a first device is connected and which produces a request for the first device; a second system which is independent from the first system; a first element which is provided in the first system and outputs the request to the second system; a second element which is provided in the second system, receives the request from the first element and outputs the request to the first system; and a third element which is provided in the first system, receives the request from the second element and outputs the request to the first device.
According to another aspect of the present invention, a method for providing an alternative path for an information processing system which includes a first system to which a first device is connected and which produces a request for the first device and a second system which is independent from the first system, wherein the first system includes a first element and a third element which is provided between the first element and the first device, wherein the second system includes a second element and: first, outputs the request from the first element to the second element; second, outputs the request from the second element to the third element; and third, outputs the request from the third element to the first device.